1. Field of the Invention
The invention relates generally to synchro devices and particularly to synchro devices wherein the synchro outputs normally require demodulation.
2. Description of the Prior Art
Synchro devices such as synchro resolvers are utilized in numerous applications for providing a measure of angular position. For example, synchro resolvers are utilized to provide an angular position feedback signal in closed loop positioning servoes. In such an application, the resolver rotor may be coupled to the element being positioned by the servo and a sinusoidal voltage, typically having a frequency of 400 Hz, applied, for example, to the resolver stator windings. The sinusoidal excitation voltage is coupled from the stator windings to the rotor output windings to provide sinusoidal output signals having respective amplitudes proportional to the sine and cosine of the angle at which the rotor is positioned. The output voltages are either in-phase or out-of-phase with the excitation voltage depending upon the angular position of the resolver rotor.
In conventional arrangements, the resolver output voltages are converted to d.c. signals of amplitude proportional to the respective sine and cosine values and of polarity in accordance with whether the output voltage is in-phase or out-of-phase with the excitation signal. Synchronous demodulators are typically utilized to perform the conversion between the sinusoidal synchro output voltages and the corresponding d.c. levels. The d.c. signals so provided may be converted into digital format by an analog-to-digital converter for numerical processing in systems utilizing a digital processor. The d.c. signals provided from the demodulators or the digitally converted versions thereof may be utilized to provide feedback signals for the closed loop servo in which the synchro resolver is utilized.
Demodulators of the type utilized with synchro devices tend to be complex, bulky and expensive and in addition require an undesired dissipation of power.
Aircraft flight instruments typically utilize a plurality of closed loop servo mechanisms to position various elements of the instrument. Each such servo mechanism may conveniently utilize a synchro resolver to provide the position feedback signal therefor. Since, in the prior art, each resolver of the type described above requires two demodulators, a considerable number of demodulators are required in such instruments. Since a decrease in power dissipation, volume, weight, complexity as well as cost is especially desirable in aircraft flight instruments, it is particularly undesirable in such an environment to utilize large numbers of demodulators.
It is a desideratum of the present invention to eliminate the requirement for demodulators in applications such as those described above.